In this paper we report the dc Kerr constant and the pretransitional temperature of a polar nematic liquid crystal 4-(trans-4’-4’-n-pentylcyclohexy)-benzonitrile (PCH-5). The observed second-order pretransitional temperature ${\mathit{T}}^{\mathrm{*}}$ from our measurements is found to be 1.2 °C below the first-order nematic to isotropic transition temperature. The dependence of the Kerr constant on (T-${\mathit{T}}^{\mathrm{*}}$${)}^{\mathrm{-}1}$ is found to be in good agreement with the predictions of the Landau–de Gennes model. The highest value of the Kerr constant observed at 632.8 nm is found to be 9.737×${10}^{\mathrm{-}11}$ m ${\mathrm{V}}^{\mathrm{-}2}$, corresponding to a temperature of 55.3 °C.

• Received 3 January 1992

DOI:https://doi.org/10.1103/PhysRevA.46.2163